Sighting in my AR-15 this weekend, found this interesting article

This is a discussion on Sighting in my AR-15 this weekend, found this interesting article within the Defensive Rifles & Shotgun Discussion forums, part of the Related Topics category; I'm going to be sighting in the iron sights on my RRA AR-15 this weekend. This in preperation of an Eotech XPS2-0 to come soon, ...

Sighting in my AR-15 this weekend, found this interesting article

I'm going to be sighting in the iron sights on my RRA AR-15 this weekend. This in preperation of an Eotech XPS2-0 to come soon, I hope. I just want to have my BUIS zero'd in just in case of an unlikely Eotech failure during a defensive situation. I read a lot of articles suggesting the 25 yard sight in, and then I ran accross this article. Sounds like this sighting in process might be a great idea. The only problem, I don't know what grain .223 or 556 he was using. I run 223 Rem Federal 55gr FMJ through my rifle. And plan on using this round 99% of the time as it's the cheapest I can find, and have about 1000 rounds in magazines ready to rock.

I'm going to be sighting in the iron sights on my RRA AR-15 this weekend. This in preperation of an Eotech XPS2-0 to come soon, I hope. I just want to have my BUIS zero'd in just in case of an unlikely Eotech failure during a defensive situation. I read a lot of articles suggesting the 25 yard sight in, and then I ran accross this article. Sounds like this sighting in process might be a great idea. The only problem, I don't know what grain .223 or 556 he was using. I run 223 Rem Federal 55gr FMJ through my rifle. And plan on using this round 99% of the time as it's the cheapest I can find, and have about 1000 rounds in magazines ready to rock.

Boy, this pretty much goes against the wealth of assembled AR-15 wisdom. If you zero at 50 yards, you are within about 2 inches of your point of aim from the muzzle out to 200 yards or so. If you zero at 25 yards, then your next zero crossing will be out to almost 300 yards but your shots will hit as much as 4 inches above your POA.

Your particular needs may dictate a "custom" zero, but my advice would be to start with the 50-yard zero and see how that works out for you. The 50-yard (50 meter for some) zero is really well-thought out and takes advantage of the relatively flat trajectory of the 5.56/.223 round, and I'm trying to understand what the 25-yard zero does for you. The whole idea behind running a red dot or reflex sight such as the EOTech or Aimpoint is to give the shooter a high probability of a hit near POA with a minimal "study" of the sight picture. With the short zero, unless you take the time to accurately estimate of measure the distance to your target, the best you will know when you pull the trigger is that your shot will hit from about 1 inch low to over 4 inches high out to 300 yards (ignoring the uncertainty introduced by the 1+ MOA center dot on the sight).

Further, you want to pretty much co-witness your BUIS with your RDS. Zeroing your BUIS at 25 yards and your RDS at 50 yards would make no sense at all; you'd need to keep mental track of different trajectories for each. Chances are, that's more than you want to be thinking about when you flip up your rear sight because the EOTech just died!

Don't forget that if you're running a standard front sight, its height is adjusted as part of the BUIS zeroing process.

Ok well lets see where to start. What barrel twist rate does your RRA have? If it is a newer rifle it probably has a 1/7 twist which is not the best for 55 grain bullets but it is workable. A 1/9 twist barrel is probably the best for that bullet weight with the 1/7 best for 62gr and above, but either or it all goes bang.

Go to the Federal website and you can download the ballistics charts for the round you are using. A 25 yard zero has/is the norm for most lets get it on paper type zero's. You get your zero and then co witness the RDS to the tip of the front site.
You still need to fire at the other distances to tweak the zero but it will be close as stated though the "zero" will not be crossing again until 300 or so yards.

Remember you will also have to compensate for the height over bore ratio at close distances, meaning on most AR's, generally speaking, there is a 1.5 -2.0 inches of difference between the height of the sight and the level of the bore which will cause the round to strike low at close range so you must adjust your point of aim accordingly.

Whatever zero you decide on zero your rifle, tweak it at different ranges, write down the results and leave it alone. Any changes made due to wind or other factors also write down so you when finished you can put the rifle back to the original settings.
Again generally speaking with a red dot type sight you will not have the time to be adding windage or elevation changes you will use holdover and holdoff to make the shot depending on what you are doing at the time.

"A first rate man with a third rate gun is far better than the other way around". The gun is a tool, you are the craftsman that makes it work. There are those who say "if I had to do it, I could" yet they never go out and train to do it. Don't let stupid be your mindset. Harryball 2013

Just remember to only adjust the front sight post which moves the strike of the round 1.25 inches per 100 meters. Keep your rear elevation at 8/3 -2 clicks for this process. The rear windage moves the strike of the round 1/2 inch per 100 meters. This should put you very close at 200 meters if using a 25 yard BZO.
Also remember the round will cross the line of sight twice.

The purpose of the 25-yd zero is that it quickly gets you zero'd without having to "hunt" all over the paper at 100 yds. I've never held to any claims that being zeroed at 25 "puts you dead on at ..." Each rifle and load is different. It's all trial and error when it comes down to it. Final zeroing should always be done at the intended range.

At what range should a rifle be zeroed? My opinion is the one that gives you the maximum "dead center" range. That means the ranges that mean the bullet will strike close enough to POA without any "correction" in aim. Certainly a .223 is flat shooting enough to shoot dead center well beyond 25 yds.

For instance, my prefered .30-06 round hit 2" high at 100yds, dead-on at 200 yds, 5" low at 300 yds. So up to @250-300 yds, if I hold "dead-on" at a deer's chest, the bullet will certainly hit it without worrying about "holdover."

OldVet, I am with you on this. The rifle dope should be verified at the anticipated range. There are so many people out there buying AR rifles that do not understand the proper way to manipulate sites is why I suggested the site adjustments. I have seen people with the rear site elevation jacked all the way up for a 100 yard zero because they don't understand the proper method of using the battle sites, which is to allow the infantry man to make quick dope changes on the battlefield as distances vary.
For my own rifle, I verify it at 200 yards using only front sight elevation and windage and then the rear elevation to compensate for any distance from 300 and beyond.
I don't know anything about electronic sites, and don't want to, as I prefer simplicity and dependability over everything else.